1hammer

: a tool that has a heavy metal head attached to a handle and that is used for hitting nails or breaking things apart

: a similar tool made usually of wood and used especially for hitting a surface to make a loud noise

: the part of a gun that strikes a charge causing the gun to shoot

Full Definition of HAMMER

1

a: a hand tool consisting of a solid head set crosswise on a handle and used for pounding

b: a power tool that often substitutes a metal block or a drill for the hammerhead

2

: something that resembles a hammer in form or action: as

a: a lever with a striking head for ringing a bell or striking a gong

b (1): an arm that strikes the cap in a percussion lock to ignite the propelling charge (2): a part of the action of a modern gun that strikes the primer of the cartridge in firing or that strikes the firing pin to ignite the cartridge